1. Field of the Invention
This invention relates to an apparatus for contact-free sensing of a moving coherent mass of material.
2. Description of Prior Art
Optical correlation speed measuring apparatuses are previously known, for example from the Swedish technical magazine Teknisk Tidskrift, 1976:3, pages 18-21. Such a known speed measuring apparatus comprises a sensing apparatus or transducer including a pair of photo-detectors and optical members (lenses, diaphragms or aperture plates, etc.) which collect heat and/or light radiation from the object whose speed is to be measured and supply it to the photo-detectors, and signal-processing means which receive output signals from the photo-detectors and derive a measure of the speed of the object to be measured. In particular the optical members are arranged so that the two photo-detectors continuously sense the varying surface structure of the object as it passes two measuring regions spaced apart a given distance (i.e. the "measuring base") in the direction of advance of the object. The photo-detector output signals supplied to the signal-processing means enable the latter to identify individual points on the surface of the advancing object. The signal-processing means, by calculating the time that it takes for a point on the object to pass the given measuring base, is thus able to provide a measure of the speed of advance of the object.
It is also known to determine or sense a dimension of an object optically, for example by reproducing the object, by means of an optical system on a detector comprising a number of photo-sensitive elements (photo-diodes or the like). By evaluation of the output signal or output signals of the detector, a measure is obtained of a dimension of the object, for example the diameter of an elongated object. A known dimension transducer of this kind is described, for example, in German Offenlegungsschrift No. 1, 923 257. The detector used in such a known dimension transducer may be designed, for example, as described in German Auslegeschrift No. 1 052 698 or as described in Electronic Design, Vol. 18, No. 22, Oct. 25, 1970, page 101.
Known measuring or sensing apparatuses of the two types mentioned above (i.e. speed measuring apparatus and dimension measuring apparatus) operate in a contact-free manner and are therefore suited for operation in severe environments and for measurement of, for example, moving objects having a high temperature where other methods of measurement cannot be used.
In certain cases it is desired to determine the volumetric flow through a cross-section of a moving coherent mass of material. An example of this is a process for supervising or controlling a stream of molten glass or molten metal flowing out of a container, where it may be necessary continuously to sense the flowing quantity of material per unit of time. Measurement of the volumetric flow of such a stream presents considerable problems, particularly since the measurement has to be made in a severe working environment. One problem is caused by the fact that the diameter of such a freely flowing molten glass or metal stream decreases continuously downwards. To obtain a good accuracy of measurement, it is therefore necessary to measure the diameter of the stream at the same region as where the speed measurement is made. However there are great difficulties in accomplishing this under the conditions which normally prevail in a process of this kind. If, for example, a correlation speed measuring apparatus is used, the apparatus typically has a measuring base of from 5 to 10 mm. However, since the diameter of the stream changes along the length of the stream, the diameter measurement should be made at precisely the right point within the measuring base and this adjustment must be maintained with high accuracy during the operation of the plant. In practice this is difficult or impossible to accomplish if completely separate instruments are used for the speed measurement and the diameter measurement. In addition readjustment must be carried out after removal or replacement of any of the separate measuring instruments, which results in a time-wasting service interruption.
The present invention aims to provide an apparatus for contact-free sensing of a moving coherent mass of material which is simple to use and economically favourable compared with known combined speed and dimension sensing apparatus.